Unloading valves for hydraulic pumps



1960 F. H. TOWLER ETAL 2,947,317

UNLOADING VALVES FOR HYDRAULIC PUMPS Filed Oct. 31, 1956 3 Sheets-Sheet1 //VVENTO FRANK HATT'I HN TOWLER JOHN MAURICE TOWLER BY M,WM &

ATTORNEYS Aug. 2, 1960 Filed Oct. 31, 1956 F. H. TOWLER ET AL UNLOADINGVALVES FOR HYDRAULIC PUMPS 3 Sheets-Sheet 2 Irze/Gxziars FY0129?Moikcvra 7501 68). fofza llflaurzloe 7E7 @561, fleceased b FY6429? 14 76w gczq Xmzby 1960 F. H. TOWLER ml. 2,947,317

UNLOADING VALVES FOR HYDRAULIC PUMPS Filed Oct. 31, 1956 3 Sheets-Sheet3 frze/erefiyrs .fiY a rzZA/a Z'ezar Ea er yO/zr? Maurglce Tea/66y,Jeceased United States Patent 2,947,311 UNLOADING VALVESFOR HYDRAULICPUWS Frank Hathom Towler, Dob Park, Otiey, England, and

John Maurice Towler, dec eased, late of Mayfair, London, England, byFrank Hathorn Towler, executor, Dob Park, Otley, England, assignors toElectraulic Presses Limited, LRodley, near Leeds, Yorkshire, England, alimited-liability fcompany of Great Britain Filed Oct. 31 1956, Ser. No.619,640 (Ilaims priority, application Great Britain June '12, 1953 14Claims. (or. 137-108) This invention relates to hydraulic systems forhydraulic presses of the type in which pressure fluid for operation ofthe press ram is supplied by more than one continuously running pump,and it has for its general object the utilization of changes of pressurein the ram cylinder to governthe operation of unloading valves to etfectthe loading and unloading of the pumps in a predetermined sequencethereby to control the speed of the press ram. This application is acontinuation-in-part of our copending application, Serial No. 435,572,filed June 9, 1954, nowabandoned.

A more specific object is to provide control mechanism operative inresponse to pressure changes from a predetermined value in a presshydraulic system for operating a rotary control valve step-by-step ineither of two directions to load or unload one or more pumps forreestablishing the predetermined pressure in the system.

Another object is to provide control mechanism of the above generalcharacter operative to maintain pressure in the system substantiallyconstant which mechanism is free of any tendency to hunt.

Still another object is to provide an automatically operating controlsystem of the vabove general character which may be present manually toload or unload one or more pumps for increasing or decreasing press ramspeed and which automatically reverts to normal automatic operation.

A further object is to provide improved drive gear for automaticallypositioning a rotary selector valve together with controls therefor-Other objects and advantages of the invention will become apparent fromthe following detailed: description of the preferred embodimentillustrated in the accompanying drawings in which Figure 1 is a somewhatdiagrammatic view illustrating a preferred form-of fluid pressureoperated drive mechanism for imparting a step-by-step motion in eitherdirection to a rotary selector valve incorporated in a press hydraulicsystem embodying the features of the invention.

Fig. 2 is a diagram illustrating the electrical control circuitassociated with the rotary selector valve and other control elements ofthe system and showing the use of a manually operated selector switchfor presetting the cutout position of the selector valve in eitherdirection of rotation.

Fig. 3 is a diagrammatic view ofa hydraulic press circuit particularlyadapted for the use of the invention.

Fig. 4 is a longitudinal sectional view through the pressure reliefvalve employed in the system shown in Fi 3. 1

Nhile we have shown and will describe herein a preferred embodiment ofthe invention, it is to be understood that this is :not intended tolimit the invention to the-particular press control organization shownbut the intention is to cover all modifications and adaptations 2falling within the spirit and scope of the invention as expressed in theappended claims.

For purposes of illustration the invention has been shown asincorporated in the hydraulic system of a hydraulic press 41 having amain press cylinder or ram 42 as shown diagrammatically in Fig. 3 of thedrawings.

In the exemplary system pressure fluid is supplied to the press cylinderby a series of pumps P, P1, P2, and P3, respectively equipped withindividual loading and unloading valves V, V1, V2, and V3. In theexemplary system, the pumps run continuously and are normally loaded,that is, they deliver their output of pressure fluid to the hydraulicsystem of the press. Each pump may be unloaded individually by operationof its associated unloading valve which diverts the pump output toexhaust in well known manner. It will be understood that the four pumpsshown are merely exemplary and that more or less than four can be usedif required. The valves V, V1, V2, and V3 are all alike and may be ofany suitable type, as for example, valves of the type shown in outPatent No. 2,655,169, issued October 13, 1953.

In the exemplary system the four pumps are arranged to discharge throughindividual check valves CV into a common pressure supply line SL whichhas a branch 43 extending to a direction control valve VD. A conduit 44connects the valve with the ram cylinder. The valve VD may be of anysuitable type adapted to connect the conduit 44 alternatively with thesupply line branch 43 or with an exhaust line 45. In the first mentionedvalve position, pressure fluid is directed to the cylinder to advancethe press ram and in the alternate position, fluid is exhausted from thecylinder to permit. retraction of the ram.

A second branch conduit 46 from the pressure supply line SL extends tocontrol means responsive to the pressure obtaining in the hydraulicsystem. This control means may conveniently take the form of a pressurerelief valve VR (Fig. 4). The branch conduit 46 also extends to a mastervalve VM, the operation of which will be explained in more detailhereinafter. Suffice it to say at this point that the master valve VMmay be similar'to that shown in our copending application, Serial No.430,339, filed May 17, 1954.

The master valve VM operates in well-known manner to determine thepressure at which the relief valve VR opens and closes by controllingfluid flow to and from a capacity chamber CC which has an operativeconnection with the valve VR. In accordance with one aspect of theinvention, the relief valve VR, in addition to relieving pressure in thesystem when required, exerts a controlling action on a selector valve SV(Fig. 3) to load or unload the pumps P, P1, P2 and P3 in predeterminedsequence for automatically maintaining selected press operating speeds.Control of the selector valve is effected through the medium of a pairof microswitches MI and MK and the control circuit showndiagrammatically in Fig. 2. The selector valve controls the loading andunloading of the pumps by regulating the operation of the valves Vl-VS.

In the particular hydraulic system illustrated the switch M] is closedwhen the pressure in the hydraulic circuit, including the ram cylinder,is at or below a predetermined value. The switch opens when the pressurerises above that value. The switch MK, on the other hand, is normallyopen and closes only when the pressure in the hydraulic circuit reachesa maximum value as determined by the rate of flow of fluid through therelief valve. i E i The selector valve SV may be of any preferred type,that shown being generally similar to the valve disclosed in our'copending application, Serial No. 342,006, now Patent No. 2,827,924,but equipped with power operated actuating means or drive gear as shownin Fig. l. Briefly, the valveis connected by conduits 50, 51, 52 and 53with the valves V, V1, V2 and V3 and controls a supply of pressure fluidfrom a control pump CF to those valves to load or unload the pumpsindividually or in predetermined combinations depending upon theposition of the movable valve member.

In the exemplary valve, the movable valve member comprises a rotarymember adapted to be turned in either direction by power operated drivegear. This drive gear, as will appear presently, is operable eithermanually under control of a selector switch S or automatically inaccordance with the opening and closing of the relief valve VR. Theinvention provides an arrangement such that turning of the valve memberin one direction from a set position, either under manual control orupon a predetermined increase of pressure in the press cylinder 42,unloads one or more of the pumps to'maintain a substantially constantoperating speed. Turning of the valve .in the opposite direction from aset position or upon a decrease in pressure in the press cylinder loadsone or more of the pumps as required to increase the pressure in thepress cylinder and maintain a substantially constant operating speed.

Referring more particularly to Figs. 1 and 3 of the drawings, the drivegear for the selector valve SV comprises a ratchet wheel I mounted onthe stem 1a by which the rotatable member or disc 1b of the valve isturned. Supported at opposite sides of the racket wheel are a pair ofpawls 2 and 3 in the form of bell crank levers pivotally supportedintermediate their ends on links 5. These links in turn are pivoted to arigid support 4.

Each of the pawls 2 and 3 has one arm positioned for operativeengagement with the ratchet wheel. The other arms of the pawls arepivotally connected respectively by links 8 with plungers 6 and 7operating respectively in cylinders 9 and 10. Each of the plungers isformed with an enlarged head 11, its inner end within the associatedcylinder presenting areas against which pressure fluid is permitted toact to force the plunger outwardly against the force exerted by returnsprings 12.

Pressure fluid is distributed to thecylinders 9 and 10 in turn throughinlets 13 under control of a solenoid operated valve 14. In the neutralposition of the valve the cylinders 9 and 10 are opened to exhaust andthe plungers are both in their inward positions in their cylinders,having been urged there by the return springs. By reason of suchpositioning the pawls are withdrawn from operative engagement with theratchet wheel 1, that is, they occupy positions corresponding to that inwhich the pawl 2 has been shown in Fig. 1.

Upon delivery of pressure fluid to a cylinder, the associated plunger isforced outwardly by the pressure acting on the enlarged area of the headand, in its advance, it causes the pawl to move upwardly and inwardlyinto engagement with the ratchet wheel 1. The ratchet wheel is thusadvanced a step equal to one tooth. A spring detent l retains theratchet wheel in seated position upon return movement of the pawl whichtakes place uponthe return of the valve 14 to neutral position. Sincethe pawls are operable selectively and act on opposite sides of theratchet wheel, it will be apparent that the ratchet wheel, and with itthe rotary valve member, may be advanced step-by-step in eitherdirectionas required. l

The valve 14 controlling the operation of the pawls 2 and 3 as shownherein is a conventional spool-type valve having a spindle 14a which ismoved in opposite directions alternately bysolenoids A and B which areenergized in a manner to be described hereinafter. Opposed center ngsprings acting on the plunger 14a normally return it to and hold it in acentral or neutral position when the operating solenoids aredeenergized. In the neutral position, both cylinders 9 and 10 areconnected to exhaust. In the operated positions one or the other of thecylinders remains connected to exhaust while the companion cylinder isconnected to a source of pressure fluid, as for example, thecontinuously running control pump CP (Fig. 3). In the exemplaryhydraulic system, the pump CP also supplies fluid to the valve SV fordistribution to the pump controlling valves V, V1, V2 and V3.

In accordance with the invention, both manual .and automatic control ofthe selector valve operating gear is effected through the medium of theelectrical control circuit shown in diagrammatic form in Fig. 2 of thedrawings.

Referring now to the diagram, it will be observed that the controlcircuit includes relays RT, RX, RY and RZ with their respective contactsCT, CX, CY and CZ. MC, MF and MH are microswitches with normally closedcontacts and ME and MG are also microswitches but with normally opencontacts. The microswitches MC, ME

and MF are mounted for coaction with the pawl 3 and microswitches MG andMH are mounted for coaction with the pawl 2, as will appear presently.The microswitches MI and MK are associated with the relief valve VR(Fig. 3) and, as previously explained the contacts of switch MK arenormally open and are only closed when the pressure in the hydrauliccircuit reaches a maximum and the flow through the relief valve exceedsa predetermined limit.

Mounted on the face of the ratchet wheel '1 are a pair of contact stripsBD and BL adapted to wipe over a series of contacts spaced apart incorrespondence with the rotational steps of the ratchet wheel and eachcorresponding to one set position of the selector valve SV.

These contacts are electrically connected with a similar set of contactsof the selector switch S which accordingly may be set manually to markany selected position of the valve. In carrying out the presentinvention, the contact and valve positions are corelated so that eachstep of the selector switch in a clockwise direction from the OEposition loads the pumps so as to add a predetermined incrementofpressure fluid to the total output. Rotation of the switch in theopposite direction decreases the pressure fluid by a similar incrementfor each step.

It will be observed that the adjacent ends of the contact strips B, Dand BL are spaced apart so that one intervening contact is left free ordead. As will appear presently the operation of the control circuit issuch that the drive gear is operated to automatically turn the valve toa position in which the contact marked by the selector switch is leftdead.

For convenience of identification the switch contacts of the controlcircuit relays have been identified with the reference characters of theassociated relays followed by a numerical suffix. The manner in whichthe relays and their switch contacts, the selector switch and solenoidsA and B are interconnected will be most readily understood from adescription of the operation of the system under the various conditionsencountered in actual use.

Idle position In the idle or off position of the apparatus, the selectorswitch S is set to mark the position in which all of the pumps areunloaded. The valve actuating ratchet wheel 1 occupies a correspondingposition with the marked contact dead, that is, between the contactstrips BD and BL. All of the relays in the control system will bedeenergized as their circuits are open at the selector switch. SolenoidsA and B are likewise deenergized and valve 14 is in neutral position.

Start To place the press in operation the selector switch finger 55 isrotated from the idle position in a clockwise direction one or moresteps to a position which marks 'asn'nsw the particular combination ofpumps to be-loaded, that is; to be placed operation. Suppose, forexample, that the press 'is to be operated'at a speed requiring theloading of three of 'the four pumps. Switch S is turned clockwise to theposition corresponding to that pump combination, say, for example, threesteps to mark the proper contact at the ratchet wheel 1. In thisposition the selector switch closes a circuit from line conductor 2,switch finger "55, selector switch and ratchet wheel contacts, contactstrip BD, conductor 29, microswitches MI, MG, and MH, normally closedcontacts CY1 of relay RY, winding relay RX to line conductor L1. RelayRX becomes energized and by closing contacts CXl'it completes anenergizing circuit for solenoid A. Relay RX also opens switch contactsCX2 to prevent anypossibility of relay RY becoming energized, Closure ofcontacts CX3 insures energization of the relay RX and solenoid A untilthe ratchet wheel has made a full step.

The energization of solenoid A shifts valve 14 to a position to directpressure fluid to the cylinder 9. The stepping pawl 2 is accordinglyadvanced to turn the ratchet wheel 1 and valve member 1b one step in thedirectionof the marked contact, i.e., in a clockwise direction. As theplunger 6 advances microswitch MG is opened first, followed by theopening of microswitch MH as the ratchet wheel completes its step. Thelatter microswitch interrupts the circuit for relay RX which becomesdeenergized and opens the circuit for solenoid A. Deenergization ofsolenoid A permits the valve 14 to return to neutral position and pawl 2is retracted by the plunger return spring.

Since "the selector switch finger 55 was moved more than one step fromthe idle position, reclosure of the switches MG and MH upon retractionof the pawl 2 will result in the reenergization of relay RX. Thestepping operation above described will be repeated, advancing theselector valve member 1b another step in the .same direction. In theassumed situation, a third step is executed in the same manner. Thisthird step carries the contact strip BD out of engagement with thecontact marked by the selector switch. Accordingly, no further steppingtakes place at this time but operation of the press will proceed withthe pumps loaded as called for by the set position of the selectorswitch.

Decrease speed-manual control Ifior. any reason it is desired todecrease the operating speed of the press, the selector switch S isturned anticlockwise one or more steps as required to establish acombination of loaded pumps with a lower volume output of pressure'fluid. Movement of the switch finger 55 from the dead contact to thenext adjacent contact complete's a circuit from line conductor L2,switch finger 55, switch and ratchet wheels contacts, contact strip BL,condutor 22, winding of relay RZ to line conductor L1. Relay RZ becomesenergized and closes its contacts CZI to energize relay RT over acircuit including normally closed microswitch MF.

Energization of relay RT completes an energizing circuit for relay RY.This circuit includes closed relay contacts CZ2, microswitches MC andME, relay contacts CT1 and CXZ. Relay RY closes contacts CYZ to completethe energizing circuit for solenoid B. The solenoid shifts valve 14 to aposition to direct pressure fluid to cylinder and the pawl 3 isaccordingly advanced to turn the ratchet wheel 1 back one step. if Itmay be noted that relay RY opens contacts CY1 to prevent inadvertentenergization of relay RX. By closing contact CYS, relay RY completes aholding circuit for solenoid B and for relay RZ independently of theselector switch. Closure ofJcontacts C Y4 completes a circuit inparallel with'that through the contacts CZ2 to insure a step of theratchet wheel. Relay RT by closing contacts CTZ entends the holdingcircuit to relay RY.

' Upon full advance of the ratchet wheel the microswitchiMF is opened bythe pawl deenergizing relay RT which'in turn opens the circuit of relayRY at contacts CTR. Relay RY becomes deenergized and opens a circuitover solenoid B at contacts CY2 and the solenoid permits valve 14 toreturn to the neutral position. The pawl 3 is then retracted by itsreturn spring and the associated microswitches are closed.

If theselector switch S has been turned only one step, the single stepof the ratchet wheel will move the contact strip BL out of engagementwith the marked contact and consequentlywill interrupt the circuit forrelay RZ. The relay then becomes deenergized and operation of the valvestepping mechanism is terminated.

When the selector switch S is turned back more than one step, additionalstepping of the ratchet wheel and selector valve takes place uponreclosure of the micro switch MP. The stepping operation is the same asthat explained above. It will be evident therefore that under normaloperating conditions, the ratchet wheel and selector valve are steppedaround until they occupy the position dictated by the setting of theselector switch S.

Increase speed-manual control The press speed may be increased manuallyat any time by simply turning the selector switch S one or more steps ina clockwise direction. The operations of the control system in that caseare precisely like those described above in connection with the startingof the press and operation.

Speed reduction by automatic pressure control When the pressure in thehydraulic system reaches a predetermined value microswitch MI is opened.Switch MK closes when the fluid flow through the relief valve reaches orexceeds a predetermined value. When microswitch MK closes, assumingswitch MP is closed, an energizing circuit is completed for relay RTwhich closes the energizing circuit for relay RY as previouslydescribed. Relay RY closes the circuit for solenoid B which initiates abackward stepping of the selector valve SV to unload a pump or pumps.Pressure in the system decreases due to the lower volume of fluiddelivered by the pumps. However, if the pressure drop is not sulficientto permit switch MK to open, the stepping operation is repeated. Thisstepping may continue if necessary until all of the pumps are unloaded,at which time switch MC opens to prevent further energization of relayRY and thus ends the backward stepping of the valve.

Automatic resetting of selected speed When press speed is automaticallyreduced as above explained the selector switch and valve, of course, getout of step. More specifically, the valve will be turned to a positionin which contact strip BD engages the contact marked by the selectorswitch. This would ordinarily call for resetting of the selector valveto load additional pumps but as long as. the excessive pressure prevailsin the system, the stepping circuit ordinarily rendered effective by theselector switch will be interrupted by the open microswitch MI. If flowthrough the relief valve drops below the predetermined volume and switchMI remains open, switch MK opens and no further change in valve settingtakes place.

When the pressure in the system drops sufficiently to allow the reliefvalve to close microswitch MI, this switch transfers control to theselector switch and initiates a clockwise stepping of the selector valveas previously described until the valve and switch S are correspondinglypositioned.

In Fig. 4 of the drawings there is shown a preferred form of the reliefvalve VR illustrating the manner in which the microswitches MI and MKmay be associated with the valve. Insofar as its pressure relievingaction is concerned this valve is structurally similar to and adapted tooperate in the same manner as the valve disclosed in our copendingapplication, Serial No. 430,-

Y blowing off through the relief valve.

339, filed May 17, 1954. More particularly, flow through the valve iscontrolled by a plunger biased to a closed position by a -light springand loaded to resist opening by pressure fluid supplied through themaster valve VM.

In addition to its pressure relieving action the valve VR is equippedwith auxiliary means for metering fluid This auxiliary metering meansprovides for actuating the microswitch MK when the fluid flow throughthe valve reaches or exceeds a predetermined volume. Microswitch MI isassociated with the valve so that it is operated when the fluid pressurein the system rises sufficiently to open the valve.

Referring more in detail to Fig. 4 of the drawings, the valve VR asshown comprises a casing 60 having a cylindrical bore 61, the upperportion of which constitutes a pressure chamber and a housing for aspring 62 acting on the shiftable plunger 63. The plunger is slidable ina valve bore 64 formed in a valve bushing 65 seated in the lower end ofthe bore 61. Valve bore 64 opens to a port 66 to which the branch 46 ofthe main pressure line is connected, It will be evident that the lowerend of the plunger is subjected to the full pressure of the fluid in thehydraulic system in which it is incorporated.

An outlet or exhaust port 67 opens laterally from the bore 64 into anannular chamber 68 in the valve casing. Thus, when the pressure exertedon the plunger 63 is sufficient to overcome the bias of the spring 62and the hydraulic load imposed on the upper end of the plunger, theplunger is shifted to establish communication between the port 66 andthe chamber 68 and the system is vented to exhaust, as will appearpresently.

Rigidly secured to the casing 60- adjacent its lower end is an auxiliarycasing 69 having a central bore 70 in communication with the chamber 68.The bore 70 has.

a lateral outlet port or exhaust 71 connected by an exhaust line to thestorage reservoir or sump of the hydraulic system. Communication betweenthe chamber 68 and the exhaust port 70 is normally closed ofl by aplunger 71 slidable in the bore 70 and urged to a closed position by aspring 72.

As shown, the plunger 71 is formed with a rearwardly extending skirtportion having an axially facing shoulder 73 adapted to abut' a steppedshoulder formed in the bore 70 to define the limit position of theplunger. pass ports 74 and 75 are provided in the head of the plunger topermit flow of fluid from the chamber 68 to exhaust when the volume issmall. Upon increase in flow above a predetermined value the pressurebuilt up in the chamber 68 forces the plunger 71 rearwardly against itsrelatively light biasing spring 72 to allow substantially unrestrictedflow to exhaust.

Rearward movement of the plunger 71 is operative to actuate themicroswitch MK. For this purpose the skirt portion of the plunger isformed with a cam surface 76 engageable by a follower 77 connected by arigid stem 78 with the switch MK. As previously explained, switch MK isnormally open and rearward movement of the plunger 71 to accommodate apredetermined volume of fluid flow to exhaust acts to close the switch.

Microswitch MI is operatively associated with the relief valve plunger63 in a manner such that the switch is opened when fluid blows offthrough the relief valve. For this purpose the switch is carried by ahousing 79 mounted within an aperture in the valve casing 60 andextending through the bushing 65 to the bore 64. An operating stem 80extending from the switch is equipped with a tapered head 81 normallyseating in a cam groove 82 formed in the plunger .63. Upon movement ofthe plunger toward open position the head 81 is 'cammed outwardly andacts to open the associated microswitch MI.

In the operation of a hydraulic press equipped with the improved controlsystem, the operating speed of the press is preset by appropriatepositioning of the manual- 1y operable selector switch S. Uponpositioning of the switch the selector valve SV is rotated to' acorresponding position by the hydraulically operated drive gear and itsassociated electrical control circuit. The'posi tioning of the selectorvalve results in the loading of one or a selected combination of aplurality of pumps, the pumps P, P1, P2 and P3 supplying pressure fluidto the hydraulic system to provide a press operating speed correspondingto that selected by the switch system.

While the press is in operation the preset operating speed isautomatically maintained by the resetting of the selector valve inaccordance with pressure changes in the hydraulic system. Such resettingis efiected under control of the relief valve VR acting through thedrive gear and its electrical control circuit. Thus, if the pressure inthe hydraulic system rises above a predetermined value, fluid blows of]?through the relief valve and the control switch MI is opened. When theblowoff of fluid reaches or exceeds a predetermined volume the controlswitch MK is closed and the drive gear operates to turn the selectorvalve SV back one step. This unloads a pump and reduces the output ofpressure fluid to the system. If the system pressure still remains toohigh, that is, if the switches MJ and MK remain actuated, the valve isturned back another step and another pump is unloaded to further reducethe pressure. This resetting may be repeated as long as required, untilcontrol of pressure is obtained or until all pumps have been unloaded.

if after such resetting of the selector valve the pressure in the systemfalls sufficiently to allow the relief valve to close, switch MI isagain actuated to cause the drive gear to turn the selector valve aheadone step. This resetting of the valve reloads a pump and correspondinglyincreases the supply of pressure fluid to the system. Should the reliefvalve remain closed the selector valve is again stepped ahead and thestepping action may be repeated until the selector valve is positionedas called for by the setting of the selector switch S.

While reference has been made to the loading and unloading of the pumpsone at a time, it will be appreciated that the change in pressure fluidoutput may be effected by loading the pumps in different combinations.This latter mode of operation is preferred when the hydraulic system isequipped with a plurality of pumps of different capacities. It will beunderstood, of course, that the correct sequence of pump loading andunloading is insured by appropriate connection of the pump unloadingvalves with the selector valve.

It will be apparent from the foregoing that the invention provides anovel and advantageous control system for hydraulic presses andcomparable hydraulic systems in which the pressure fluid is supplied bya plurality of continuously running pumps. Loading of one or more of thepumps to provide a desired press speed is effected quickly and easily bythe setting of a manually operable selector switch. Moreover,substantial uniformity of press speed is maintained automatically bypressure responsive valve means which serves to load or unload pumps asrequired to maintain substantially uniform pressure in the system. Theinvention provides novel means in the form of a selector valve and poweroperated driving means therefor by which the setting of the selectorvalve is effected. In general, therefore, optimum operating conditionsare established and maintained in a simple, expeditious manner insuringeflicient operation of the press at all times.

We claim as our invention:

1. Ina hydraulic system supplied with pressure fluid from a plurality ofsources, in combination, an unloading valve individual to each fluidsource eflective when operated to divert the fluid from the source toexhaust, a multi-position selector valve operatively connected with eachof the unloading valves, said selector valve "an-ma ia being settableinselected positionsi'each of which represents a particular number-ofefiective fluid sources, power operated means for moving said selectorvalve from one position to another, a relief valve in the hyraulicsystem'operative to divertfluidto exhaust when the pressure in thesystem rises to a predetermined value, and control means operable inresponse to the flow through the relief valve exceeding a predeterminedvolume for initiating operation of said power operated means to movesaid selector valve in a direction to operate an additionalunloadingvalve or valves and reduce the number of effective fluidsources.

2. In a hydraulic system suppliedwith pressure fluid from a plurality ofsources, in combination,an unloading valve individual to eachfluidsource adapted when operatedto divert the fluid from the source toexhaust, a multi-position selector valve operatively connected with theunloading valves, said selector valve being settable in selectedpositions each of which represents a particular number of effectivefluid sources, power operated means for moving saidsele'ctor valve fromone position to another, a relief valve in the hydraulic systemoperative to divert fluid to exhaust when the pressure in the systemrises to a predetermined value, auxiliary valve means connected toreceive the fluid diverted by' said relief valve and adapted to openvarying degrees according to the volume of fluid diverted, and meansactuated by said auxiliary valve when the volume of fluid reaches apredetermined value for initiating the operation of said power operatedmeans to move said selector valve in a direction eifective to reduce thenumber of effective fluid sources.

3. In a hydraulic system supplied with pressure fluid from a pluralityof sources, in combination, an unloading valve individual to each fluidsource adapted when operated to divert the fluid fromthe source toexhaust, a multi-position selector 'valve operatively connected witheach of the unloading valves, said selector valvebeing settable inselected positions in each of which it acts to operate a particularcombination of unloading valves to determine the number of effectivefluid sources, power operated means for moving said selector valve fromone position 'to another, a relief valve in the hydraulic systemoperative to divert fluid to'exhaust when the pressure in the systemrises to a predetermined value, control means operable in response tothe fluid diverted through the relief valve exceeding a predeterminedvolume to initiate the operation of said power operated means for movingthe selector valve in a direction effective to reduce the number ofeffective fluid sources, said control means cooperating with othercontrol means actuated by said relief valve when the pressure in thesystem falls below said predetermined value for initiating operation ofsaid power operated means to move said selector valve in a directioneffective to increase the number of effective fluid sources.

4. In a hydraulic system supplied with pressure fluid from a pluralityof sources, in combination, an unloading valve individual to each sourceadapted when operated to divert the fluid from the source to exhaust, amultiposition selector valve operatively connected with each of theunloading valves, said selector valve having a member rotatable toselected positions in each of which it is efiectiveto operate one or acombination of the unloading valves to determine the number of effectivefluid sources, drive means for said valve including a ratchet wheelfixed to the rotatable *valve'member, a bell crank lever having a pawlon one of its arms engageable with the teeth of the ratchet wheel, alink pivoted at one end on a stationary part of the valve gear andpivoted at its other end to the intermediate portion of said bell crank,an actuator connected with the other arm of said bell crank operable toshift the same between a retracted and an advanced position, the pivotalconnection between said link and said bell crank being located so thatin the initial movement "of said actuator from retracted position thebell crank is rocked about that pivotal connection to engage said pawlwith the teeth of "theratchet wheel, further movement of said actuatorbeing operative to rock said link about its pivot and to shift said bellcrank body ina direction to impart a rotative step to said ratchetwheel.

5. Ahydraulic system as defined in claim 4 in which the selector drivemeans also includes a second pawl carrying bell crank lever and anactuator positioned to coact withthe ratchet wheel and operative toimpart step-bystep rotative movement thereto in a direction opposite tothat imparted by the first-mentioned pawl carrying bell crank lever.

6. A hydraulic system as defined in claim 4'in which the actuator forthe pawl carrying bell crank lever comprises a cylinder with a workingpiston spring biased to one position and shiftable to an "alternateposition upon introduction of pressure fluid into the cylinder.

7. A hydraulic system as defined in claim 5 in which the actuators forthe pawl carrying bell cranks are "pressure fluid operated and in whichthe operation of the actuators' is controlled by a second selectorvalve.

8. A hydraulic system as defined in claim 7 in which the second selectorvalve is normally biased to a neutral positionto shut off fluid flow tothe actuators and is shiftable to either of two operative positions byseparate solenoids to direct fluid flow to one or the other of theactuators individually.

9. in a hydraulic system supplied with pressure fluid from a pluralityof sources, in combination, an unloading valve individual to each fluidsource adapted when operated to divert the fluid from the source toexhaust, amulti-position selector valveoperatively connected with eachof the unloading valves, said selector valve having a member rotatableto selected positions to determine the number of unloading valvesoperated, drive means for said selector valve including a ratchet wheelfixed to and rotatable with the valve member, first and second pawl andratchet mechanisms operative respectively to impart step-by-steprotative movement to said ratchet wheel in opposite directions, apressure fluid operator for each mechanism, a valve connected to controlthe operation'of said actuators, a first solenoid operative whenener'gized to shift said control valve to a position to initiate theoperation of one of said actuators, a second solenoid operative whenenergized to shift said control valve to a position to initiate theoperationof the other of the said actuators, means for establishing anoperating circuit for each solenoid including a contact strip mounted onrotatable with said ratchet wheel, a series of stationary contacts eachrepresentative of a particular position of said ratchet wheel, saidcontacts being arranged for en gagement successively by said strips inthe rotation of the ratchet wheel, and a manually operative switchadapted to close the circuit through any one of the selected contacts,the solenoid associated with the strip engaging the selected contactbeing energized to initiate the operation of the associated actuator torotate said ratchet wheel to the position represented by the selectedcontact.

10. In a-hydraulic system supplied with pressure fluid from a pluralityof sources, in combination, an unloading valve individual to each fluidsource, adapted when operated to divert the fluid from the source toexhaust, the combination of a multi-position selector valve operativelyconnected with each of the unloading valves, said selector valve havinga member rotatable to selected positions to determine the number ofunloading valves operated, drive means for said selector valve includinga ratchet wheel iixed to and rotatable with the valve member, first andsecond pawl and ratchet mechanisms operative respectively to impartstep-by-step rotative movement to said ratchet wheel in oppositedirections, a pressure fluid operator for each mechanism, a valveconnected to control the operation of said actuators, a first solenoidoperative when energized to shift said control valve to a position toinitiate the operation of one of said actuators, a second solenoidoperative when energized to shift said control valve to a position toinitiate the operation of the other of the said actuators, means forestablishing an operating circuit for each solenoid including a contactstrip mounted on and rotatable with said ratchet wheel, a series ofstationary contacts each representative of a particular position of saidratchet wheel, said contacts being arranged for engagement successivelyby said strips in the rotation of the ratchet wheel, a manuallyoperative switch adapted to close a circuit through any selected one ofthe said contacts, the solenoid associated with the strip engaging theselected contact being energized to initiate the operation of theassociated actuator to rotate said ratchet'wheel to the positionrepresented by the selected contact and a supplementary switch operableto initiate the operation of one of said actuators to step the ratchetwheel away from the position represented by the selected contact.

11. In a hydraulic system supplied with pressure fluid from a pluralityof sources, in combination, an unloading valve individual to each fluidsource adapted when operated to divert the fluid from the source toexhaust, the combination of a multi position selector valve operativelyconnected with each of the unloading valves, said selector valve havinga member rotatable to selected positions to determine the number ofunloading valves operated, drive means for saidvalve including a ratchetwheel fixed to and rotatable with the valve member, first and secondpawl and ratchet mechanisms operative respectively'to impartstep-by-step rotative movement to said ratchet wheel in oppositedirections, a pressure fluid operator for each mechanism, a valveconnected to control the operation of said actuators, a first solenoidoperative when energized to shift said control valve to a position toinitiate the operation of one of said actuators, a second solenoid.operative when energized to shift said control valve to a position toinitiate the operation of the other of the said actuators, means forestablishing an operating circuit for each solenoid including a contactstrip mounted on and rotatable with said ratchet Wheel, a series ofstationary contacts each representative of a particular position of saidratchet wheel, said contacts being arranged for engagement successivelyby said strips in the rotation ofthe ratchet Wheel, a switch settablemanually to close a circuit through any selected one of said contacts,the solenoid associated with said strip engaging the selected contactbeing energized to initiate the operation of the associated actuator torotate said ratchet wheel to the position represented by the selectedcontact, and a switch operable when the pressure in the system exceeds apredetermined value for initiating operation of one of said actuators toimpart a step to the ratchet wheel eflective to position said valve forreducing the number of unloading valves operated.

12. In a hydraulic system having a plurality of fluid sources supplyingfluid under pressure to a common supply line and an individual unloadingvalve associated with each fluid source adapted when operated to directthe fluid from the source to exhaust, a control system'including aselector valve operatively connected with each of the unloading valvesand rotatable to different positions to operate said unloading valves indifferent combinations, power operated means for rotating said selectorvalve step-by-step, a control circuit including a manually operableselector switch having a plurality of positions corresponding to thepositions of said selector valve, said control circuit being operativeupon the setting of the switch in a selected position for initiatingoperation of said drive mechanism to rotate said valve to acorresponding posi: tion, valve 'means responsive to the pressure insaid sup: ply line, a'ndswitch means actuated by said valve means forinitiating the operation of said drive mechanism to shift said valvefrom its set position to a new position when the pres-sure in the linevaries trom a predetermined value.

13. In a hydraulic system having a plurality of fluid sources supplyingfluid under pressure to a common supply line and an individual unloadingvalve associated with each fluid source adapted when operated to directthe fluid from the source to exhaust, a control system including aselector valve operatively connected with each of the unloading valvesand rotatable to different positions to operate said unloading valves indifferent combinations, power operated means for-rotating said selectorvalve step-by-step, a control circuit including a manually operableselector switch having a plurality of positions corresponding to thepositions of said selector valve, said control circuit being operativeupon the setting of the switch in a selected position for initiatingoperation of said drive mechanism to rotate said valve to acorresponding position, a relief valve connected to said supply lineoperative to divert fluid from the line to exhaust when the pressureexceeds a predetermined value, and means including a switch actuatedwhen the volume of fluid diverted by said relief valve exceeds apredetermined value for initiating the operation of said drive mechanismto shift said valve in a direction to increase the number of unloadingvalves operated. "14. In a hydraulic system having a plurality of fluidsources supplying fluid under pressure to a common supply line and anindividual unloading valve associated with each fluid source adaptedwhen operated to direct the fluid from the source to exhaust, a controlsystem including a selector valve operatively connected with each of theunloading valves =and rotatable to difierent positions to operatesaidvalves in difierent combinations, power operated means for rotating saidvalve step-by-step, a control circuit including a manually operableselector switch having a plurality of positions corresponding to thepositions of said valve, said control circuit being operative upon thesetting of the switch in a selected position for initiating operation ofsaid drive mechanism to rotate said valve to a corresponding position, apressure responsive valve connected to said supply line operative upon apre determined pressure rise in the line for initiating the operation ofsaid drive mechanism to shift said valve in a direction to increase thenumber of unloading valves operated.

References Cited in the file of this patent UNITED STATES PATENTSAustralia Dec. 2, 1955

